WFContent serialized field = path. But in fact ID is more static then path. For example WFContent referencing an user but the user has been moved to a different path. In that case when a flow wakes up it's going to abort. But if it would have used ID then things would have continued on, cause ID hasn't changed only the path.
https://github.com/SenseNet/sn-workflow/blob/e2b963c528c17f02ac31835b129b9a068ebf2f61/src/Workflow/WfContent.cs#L24
WFContent serialized field = path. But in fact ID is more static then path. For example WFContent referencing an user but the user has been moved to a different path. In that case when a flow wakes up it's going to abort. But if it would have used ID then things would have continued on, cause ID hasn't changed only the path.